IPAC2017 - List of Authors (Repond, J.)

Paper	Title	Page
WEPIK089	Characterization of Resonant Impedances of CERN-SPS Gate Valves	3139
	T. Kaltenbacher, J. Repond, C. Vollinger CERN, Geneva, Switzerland
	For the CERN High Luminosity LHC project, a doubling of bunch intensity is foreseen. However, this intensity increase is currently limited by the LHC injector chain, in part due to longitudinal multi-bunch instabilities in the SPS. Therefore, the implementation of an accurate SPS impedance model was started some time ago in order to obtain a better understanding of instability sources and develop mitigation measures. In this paper, we present the electromagnetic characterization of commonly used all-metal gate valves with respect to their contribution to the SPS longitudinal impedance. The valve impedance was evaluated with commercially available EM-field simulation programs and verified with RF-bench measurements. Using this input, it was possible to obtain in particle simulations the dependence of the multi-bunch stability threshold on the number of these valves. A practical means of mitigation is to use a commercially available impedance shielded version of these gate valves. We also present the associated reduction in beam coupling impedance and the expected gain in beam stability if all existing unshielded valves are replaced by shielded valves.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK089
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THPVA022	Comparison of Different Methods to Calculate Induced Voltage in Longitudinal Beam Dynamics Codes	4465
	D. Quartullo, J. Repond CERN, Geneva, Switzerland M. Migliorati University of Rome La Sapienza, Rome, Italy
	Collective effects in longitudinal beam dynamics simulations are essential for many studies since they can perturb the RF potential, giving rise to instabilities. The beam induced voltage can be computed in frequency or time domain using a slicing of the beam profile. This technique is adopted by many codes including CERN BLonD. The slicing acts as a frequency filter and cuts high frequency noise but also physical contributions if the resolution is not sufficient. Moreover, a linear interpolation usually defines the voltage for all the macro-particles, and this can be another source of unphysical effects. The MuSiC code describes interaction between the macro-particles with the wakes generated only by resonator impedances. The complications related to the slices are avoided, but the voltage can contain high frequency noise. In addition, since the computational time scales with the number of resonators and macro-particles, having a large number of them can be cumbersome. In this paper the features of the different approaches are described together with benchmarks between them and analytical formulas, considering both single and multi-turn wakes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA022
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Characterization of Resonant Impedances of CERN-SPS Gate Valves

3139

T. Kaltenbacher, J. Repond, C. Vollinger
CERN, Geneva, Switzerland

For the CERN High Luminosity LHC project, a doubling of bunch intensity is foreseen. However, this intensity increase is currently limited by the LHC injector chain, in part due to longitudinal multi-bunch instabilities in the SPS. Therefore, the implementation of an accurate SPS impedance model was started some time ago in order to obtain a better understanding of instability sources and develop mitigation measures. In this paper, we present the electromagnetic characterization of commonly used all-metal gate valves with respect to their contribution to the SPS longitudinal impedance. The valve impedance was evaluated with commercially available EM-field simulation programs and verified with RF-bench measurements. Using this input, it was possible to obtain in particle simulations the dependence of the multi-bunch stability threshold on the number of these valves. A practical means of mitigation is to use a commercially available impedance shielded version of these gate valves. We also present the associated reduction in beam coupling impedance and the expected gain in beam stability if all existing unshielded valves are replaced by shielded valves.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK089

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPVA022

Comparison of Different Methods to Calculate Induced Voltage in Longitudinal Beam Dynamics Codes

4465

D. Quartullo, J. Repond
CERN, Geneva, Switzerland
M. Migliorati
University of Rome La Sapienza, Rome, Italy

Collective effects in longitudinal beam dynamics simulations are essential for many studies since they can perturb the RF potential, giving rise to instabilities. The beam induced voltage can be computed in frequency or time domain using a slicing of the beam profile. This technique is adopted by many codes including CERN BLonD. The slicing acts as a frequency filter and cuts high frequency noise but also physical contributions if the resolution is not sufficient. Moreover, a linear interpolation usually defines the voltage for all the macro-particles, and this can be another source of unphysical effects. The MuSiC code describes interaction between the macro-particles with the wakes generated only by resonator impedances. The complications related to the slices are avoided, but the voltage can contain high frequency noise. In addition, since the computational time scales with the number of resonators and macro-particles, having a large number of them can be cumbersome. In this paper the features of the different approaches are described together with benchmarks between them and analytical formulas, considering both single and multi-turn wakes.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA022

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)